阅读说明：本技术 基于热弹效应的金属表面裂纹位置及大小的识别方法 (Method for identifying position and size of metal surface crack based on thermoelastic effect ) 是由 史维佳 赵勃 谭久彬 于 2021-09-02 设计创作，主要内容包括：本发明公开了一种基于热弹效应的金属表面裂纹位置及大小的识别方法,包括：在待测材料表面上选择入射点,并确定位置接收点；基于热弹效应,使激光在入射点入射材料表面,表面波沿着表面进行传播,当表面波遇到裂纹时产生反射表面波；以激光开始入射为时间零点记录位置接收点第一次接收到表面波所用时刻,当有反射表面波存在时,记录位置接收点接收到反射表面波的时间,分别求解表面波的波速、裂纹的位置；当表面波到达裂纹底部时,表面波转换为反射横波在材料内部传播,记录位置接收点接收到反射横波的时间,以求解裂纹的高度。该方法可在确定待测缺陷金属件的表面裂纹缺陷是否存在的同时,能够定量表征表面裂纹缺陷的深度以及具体位置。(The invention discloses a method for identifying the position and size of a crack on the surface of a metal based on a thermoelastic effect, which comprises the following steps: selecting an incident point on the surface of a material to be detected, and determining a position receiving point; based on the thermo-elastic effect, laser is made to enter the surface of the material at an incident point, surface waves propagate along the surface, and when the surface waves encounter cracks, reflected surface waves are generated; recording the time when the position receiving point receives the surface wave for the first time by taking the laser starting incidence as a time zero point, recording the time when the position receiving point receives the surface wave when the surface wave exists, and respectively solving the wave velocity of the surface wave and the position of the crack; when the surface wave reaches the bottom of the crack, the surface wave is converted into a reflected transverse wave to propagate in the material, and the time for receiving the reflected transverse wave by the receiving point at the position is recorded so as to solve the height of the crack. The method can quantitatively represent the depth and the specific position of the surface crack defect while determining whether the surface crack defect of the metal piece with the defect to be detected exists.)

1. A method for identifying the position and size of a crack on a metal surface based on a thermoelastic effect is characterized by comprising the following steps:

step S1, selecting a laser incidence point on the surface of a material to be detected, and determining a position m away from the laser incidence point as a position receiving point of the surface of the material to be detected, wherein m is a positive number;

step S2, based on the thermo-elastic effect, making laser incident on the surface of the material to be measured at the laser incident point, propagating surface waves along the surface of the material to be measured, and generating reflected surface waves when the surface waves encounter cracks;

step S3, recording the time taken by the position receiving point to receive the surface wave for the first time with the laser start to enter as a time zero point, recording the time taken by the position receiving point to receive the surface wave when the surface wave exists, and respectively solving the wave velocity of the surface wave, the position of the crack, and the distance from the position receiving point to the crack;

and step S4, converting the surface wave into a reflected transverse wave to propagate in the material when the surface wave reaches the bottom of the crack, and recording the time when the position receiving point receives the reflected transverse wave so as to solve the height of the crack.

2. The method of claim 1, wherein two surface wave signals are received if the position receiving point is between the crack and the laser incidence point.

3. The method for identifying the position and size of the crack on the metal surface based on the thermo-elastic effect according to claim 1, wherein the wave speed of the surface wave R is as follows:

wherein v is_RM is the distance between the laser incident point and the position receiving point, T₁The time taken for the first reception of the surface wave by the location reception point.

4. The method for identifying the position and the size of the crack on the metal surface based on the thermo-elastic effect is characterized in that the position of the crack is as follows:

wherein x is the position of the crack, v_RIs the wave velocity, T, of said surface wave₂And m is the time when the position receiving point receives the reflected surface wave, and the distance between the laser incidence point and the position receiving point.

5. The method for identifying the position and the size of the crack on the metal surface based on the thermo-elastic effect according to claim 1, wherein the distance from the position receiving point to the crack is as follows:

wherein n is a distance from the position receiving point to the crack, m is a distance between the laser incidence point and the position receiving point, and T is₁For the time, T, taken by the receiving point at said position to receive the surface wave for the first time₂The time at which the reflected surface wave was received for the location receiver point.

6. The method for identifying the position and the size of the crack on the metal surface based on the thermo-elastic effect is characterized in that the height of the crack is as follows:

wherein, T₁For the time, T, taken by the receiving point at said position to receive the surface wave for the first time₂Time of reception of said reflected surface wave for said location reception point, T₃And m is the time when the position receiving point receives the reflected transverse wave, and the distance between the laser incidence point and the position receiving point.

Technical Field

The invention relates to the technical field of nondestructive testing, in particular to a method for identifying the position and size of a crack on the surface of a metal based on a thermoelastic effect.

Background

The ultrasonic nondestructive testing technology is widely applied to the fields of aerospace equipment in-service testing, nuclear industry equipment reliability testing and the like. The ultrasonic nondestructive detection technology comprises a piezoelectric ultrasonic nondestructive detection technology, a magnetostrictive ultrasonic nondestructive detection technology and a laser ultrasonic nondestructive detection technology. The piezoelectric ultrasonic technology generates ultrasonic waves by contacting a piezoelectric transducer with the surface of a workpiece, and is widely applied. For some special occasions, such as the surface to be measured is too small to place a transducer, or a special environment cannot directly contact with an object to be measured, the piezoelectric ultrasonic technology cannot be effectively applied. The magnetostrictive ultrasonic nondestructive testing technology is characterized in that a magnetic field is excited on the surface of a metal object to be tested, so that the metal generates micro deformation to generate ultrasonic waves, and the ultrasonic nondestructive testing technology has special requirements on the material of the object to be tested and has limitation in application. The laser ultrasonic detection based on the thermoelastic effect is a non-contact ultrasonic nondestructive method, has the advantages of high sensitivity and high bandwidth, and is applied to the fields of weld joint detection, metal crack detection, composite material detection and the like.

In the nineties of the last century, the laser ultrasonic detection technology based on the thermoelastic effect is firstly applied to pipeline crack detection, and then the laser ultrasonic technology is continuously developed and applied in more fields. A laser ultrasonic detection method for micro-defects is proposed by special equipment supervision and inspection technology research institute in Shanghai city, and relates to a laser ultrasonic detection method for micro-defects, which comprises the following steps: the laser probe emits pulse laser to obliquely act on a workpiece to be measured; placing the air coupling probe on the same side of the laser probe and vertically facing the surface of the workpiece to be measured, and adjusting the distance between the air coupling probe and the surface of the workpiece to be measured to receive scattered signals generated due to material defects; and judging the defects in the material by the scattered signals received by the air coupling probe. The method can overcome the influence of the blind area, is suitable for detecting the defects of thin workpieces and near surfaces, and has the advantages of simple detection process, machine control of the detection process and good repeatability. But this method cannot determine the specific location and size of the defect.

The invention discloses a system for detecting the surface defects of a pipeline based on laser ultrasound, which comprises a water cooling device, a pulse laser generator, a laser excitation probe, a two-dimensional mobile platform, an ultrasonic detection probe, an optical fiber separator, a dual-wave mixing interferometer, a signal amplifier, a data acquisition card, terminal equipment and a waveform display module, wherein light beams emitted by the pulse laser generator are reflected by the laser excitation probe and then vertically irradiate the surface of the pipeline to be detected; the pipeline to be measured is placed on a movable two-dimensional moving platform; the light beam reflected by the tested pipeline is emitted into the ultrasonic detection probe, and enters the optical fiber separator and the double-wave hybrid interferometer after being reflected by the ultrasonic detection probe; and then the terminal equipment obtains the surface defect parameters of the measured pipeline according to the ultrasonic signals after the amplification and filtering processing. By utilizing the system, the information such as the depth, the angle and the like of the surface defect of the pipeline can be effectively detected, and the detection efficiency of the pipeline defect is improved. But this method cannot determine the location and size of the surface cracks.

In summary, the existing detection means for metal surface crack defects are continuously developed, and it can be generally determined whether the surface crack defects of the metal piece with the defects to be detected exist, but the depth and the specific positions of the surface crack defects cannot be quantitatively characterized. The detection of the position and size of the surface defect is generally applied to the qualification evaluation of a manufactured part and whether a certain component of in-service equipment needs to be replaced and maintained, so that a convenient and feasible surface crack shape identification method is needed for the application requirements.

Disclosure of Invention

The present invention is directed to solving, at least to some extent, one of the technical problems in the related art.

Therefore, the invention aims to provide a method for identifying the position and the size of a metal surface crack based on the thermoelastic effect, which can quantitatively represent the depth and the specific position of the surface crack defect while determining whether the surface crack defect of a metal part to be detected exists.

In order to achieve the above object, an embodiment of the present invention provides a method for identifying a position and a size of a crack on a metal surface based on a thermo-elastic effect, including the following steps: step S1, selecting a laser incidence point on the surface of a material to be detected, and determining a position m away from the laser incidence point as a position receiving point of the surface of the material to be detected, wherein m is a positive number; step S2, based on the thermo-elastic effect, making laser incident on the surface of the material to be measured at the laser incident point, propagating surface waves along the surface of the material to be measured, and generating reflected surface waves when the surface waves encounter cracks; step S3, recording the time taken by the position receiving point to receive the surface wave for the first time with the laser start to enter as a time zero point, recording the time taken by the position receiving point to receive the surface wave when the surface wave exists, and respectively solving the wave velocity of the surface wave, the position of the crack, and the distance from the position receiving point to the crack; and step S4, converting the surface wave into a reflected transverse wave to propagate in the material when the surface wave reaches the bottom of the crack, and recording the time when the position receiving point receives the reflected transverse wave so as to solve the height of the crack.

The method for identifying the position and the size of the metal surface crack based on the thermoelastic effect can detect the micro crack existing on the surface of the material, has a good detection effect on the micro crack with the size within the ultrasonic sound wave length range, and can effectively identify the position and the size of the crack by analyzing different types of ultrasonic signals in the material.

In addition, the method for identifying the position and the size of the metal surface crack based on the thermo-elastic effect according to the above embodiment of the invention may further have the following additional technical features:

further, in one embodiment of the present invention, if the position reception point is between the crack and the laser incidence point, the surface wave signal is received twice.

Further, in an embodiment of the present invention, the wave speed of the surface wave R is:

wherein v is_RM is the distance between the laser incident point and the position receiving point, T₁The time taken for the first reception of the surface wave by the location reception point.

Further, in one embodiment of the present invention, the position of the crack is:

wherein x is the position of the crack, v_RIs the wave velocity, T, of said surface wave₂And m is the time when the position receiving point receives the reflected surface wave, and the distance between the laser incidence point and the position receiving point.

Further, in one embodiment of the present invention, the distance from the position receiving point to the crack is:

wherein n is a distance from the position receiving point to the crack, m is a distance between the laser incidence point and the position receiving point, and T is₁For the time, T, taken by the receiving point at said position to receive the surface wave for the first time₂The time at which the reflected surface wave was received for the location receiver point.

Further, in one embodiment of the present invention, the height of the crack is:

wherein, T₁For the time, T, taken by the receiving point at said position to receive the surface wave for the first time₂Time of reception of said reflected surface wave for said location reception point, T₃Receiving the reflection for the location reception pointAnd m is the distance between the laser incidence point and the position receiving point.

Additional aspects and advantages of the invention will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the invention.

Drawings

The foregoing and/or additional aspects and advantages of the present invention will become apparent and readily appreciated from the following description of the embodiments, taken in conjunction with the accompanying drawings of which:

FIG. 1 is a diagram of laser ultrasound sound based on the thermo-elastic effect according to an embodiment of the present invention;

FIG. 2 is a flow chart of a method for identifying the location and size of a crack on a metal surface based on the thermo-elastic effect according to an embodiment of the present invention;

FIG. 3 is a laser ultrasonic flaw detection view of one embodiment of the present invention;

FIG. 4 is a diagram illustrating displacement of the probe point in the Y direction according to an embodiment of the present invention;

FIG. 5 is a schematic view of a crack bottom reflected shear wave according to an embodiment of the present invention;

fig. 6 is a graph of laser pulse temporal distribution and spatial distribution according to one embodiment of the present invention.

Detailed Description

Reference will now be made in detail to embodiments of the present invention, examples of which are illustrated in the accompanying drawings, wherein like or similar reference numerals refer to the same or similar elements or elements having the same or similar function throughout. The embodiments described below with reference to the drawings are illustrative and intended to be illustrative of the invention and are not to be construed as limiting the invention.

The embodiment of the invention emits laser pulses to the surface of a material to be measured, generates temperature gradients on an incident surface and a subsurface, and excites different types of ultrasonic waves such as longitudinal waves, transverse waves and surface waves at an incident point due to the thermo-elastic effect of the material. As shown in fig. 1, in laser ultrasound based on the thermo-elastic effect, R, S, and L in the figure represent a surface wave, a transverse wave, and a longitudinal wave, respectively, in which the longitudinal wave has the fastest propagation speed and relatively small amplitude, the surface wave has large amplitude in the propagation direction along the surface of the object, and the transverse wave and the surface wave have similar wave speeds. Because the properties of the surface wave, the longitudinal wave and the transverse wave are different and easy to distinguish, the embodiment of the invention utilizes various ultrasonic waves of different types to complete the identification work of the position and the size of the crack on the metal surface.

The method for identifying the position and size of the crack on the metal surface based on the thermo-elastic effect according to the embodiment of the invention is described below with reference to the accompanying drawings.

FIG. 2 is a flow chart of a method for identifying the position and size of a crack on a metal surface based on the thermo-elastic effect according to an embodiment of the invention.

As shown in fig. 2, the method for identifying the position and size of the crack on the metal surface based on the thermo-elastic effect comprises the following steps:

in step S1, a laser incidence point is selected on the surface of the material to be measured, and a position receiving point which is m, which is a positive number, apart from the laser incidence point is determined as the surface of the material to be measured.

Specifically, as shown in fig. 3, the high-power narrow-pulse laser is incident on the surface of the material to be measured from the laser incident point, and a detection point (i.e., a position receiving point) is located near the incident point and is used for detecting the displacement perpendicular to the surface of the material. When laser is irradiated on the surface of a material to be detected, laser energy is mainly converted into heat energy, so that a temperature gradient exists in the material, and ultrasonic waves are excited at a laser incidence point due to the thermo-elastic effect of the material.

In step S2, laser light is made incident on the surface of the material to be measured at the laser incident point based on the thermo-elastic effect, the surface wave propagates along the surface of the material to be measured, and when the surface wave encounters a crack, a reflected surface wave is generated.

Further, as can be seen from fig. 3, the surface wave R propagates along the surface of the object after being excited by the incident point, and a reflected surface wave Rr is generated when the surface wave encounters a crack, so that two surface wave signals are received when the signal receiving probe point is between the crack and the laser incident point. As shown in fig. 4, when comparing the Y-direction displacement diagram of the material surface received by the position receiving point with the Y-direction displacement diagram of the material surface without cracks and cracks at different positions, only the longitudinal wave L and the laser-excited surface wave R can be observed in the diagram when the reflected surface wave signal is not received at the detecting point; when the surface of the material has a crack defect, the detection point receives a reflected surface wave signal, and the farther the crack is away from the detection point, the later the reflected surface wave is received.

In step S3, the time taken for the recording position reception point to receive the surface wave for the first time is recorded with the start of incidence of the laser as the time zero point, and when there is a reflected surface wave, the time at which the recording position reception point receives the reflected surface wave is recorded, and the wave velocity of the surface wave, the position of the crack, and the distance from the position reception point to the crack are determined.

Specifically, the time T1 taken by the probe point to receive the surface wave for the first time is recorded with the time zero point at which the laser beam starts to enter, the time T2 taken by the probe point to receive the surface wave when there is a surface wave present is recorded, and the wave velocity of the surface wave can be obtained by knowing that the distance between the laser beam entering point and the signal receiving point is m:

from the wave speed v of the surface wave_RAnd the time T2 when the probe point receives the reflected surface wave can obtain the position x of the surface crack as:

in step S4, when the surface wave reaches the bottom of the crack, the surface wave is converted into a reflected transverse wave and propagates inside the material, and the time when the position receiving point receives the reflected transverse wave is recorded to solve the height of the crack.

Specifically, as shown in fig. 5, when the laser-excited surface wave R encounters a crack, the surface wave R propagates along the crack surface, and when the surface wave reaches the bottom of the crack, it is converted into a reflected transverse wave RS that propagates inside the material.

The time for receiving the bottom surface reflected transverse wave by the receiving point at the recording position is T3, which can be obtained from the geometrical relationship of FIG. 5:

wherein T2 is the time of the position receiving point receiving the surface wave, h is the height of the crack, beta is the included angle between the crack and the surface of the material to be measured, s is the distance from the bottom of the crack to the detecting point, v_RIs the wave velocity, v, of a surface wave_SThe wave velocity of the bottom reflected transverse wave is shown, and n is the distance from the detection point to the crack.

Knowing the time T1 taken by the probe point to receive the surface wave for the first time, the time T2 taken by the probe point to receive the reflected surface wave, the time taken by the probe point to receive the bottom reflected transverse wave is T3, and the distance n from the probe point to the crack is given by the equations (1) and (2):

mu is the Poisson's ratio of the material, and can be known from the theory of solid mechanics

For an actual material crack, the included angle β between the actual material crack and the surface of the material is about 90 °, and sin β is 1 to compensate for the error introduced by the speed of the surface wave instead of the speed of the shear wave. Substituting equations (1), (4) and (5) into equation set (3) can obtain the height h of the crack as:

the method for identifying the position and size of the crack on the metal surface based on the thermo-elastic effect is further described below with reference to specific examples.

The crack position detection step is described by taking fig. 3 as an example. Selecting a certain point on the material to be detected as a laser incidence point, and arranging a material surface displacement detection point at a distance of m from the incidence point.

Setting the appropriate laser pulse spot radius and pulse time, wherein the time and space distribution functions of the laser pulse are respectively as follows:

fig. 6 shows the laser time and spatial distribution function of the detection range within 10mm, wherein the spot diameter is 30um and the pulse rise time is 10 ns.

The laser pulse is emitted while the signal begins to be received at a probe point on the surface of the material. Recording the received signal, and observing the signal waveform received by the detection point. If the surface wave signal is received only once, the fact that no surface crack exists near the detection point is indicated, and the incident position of the laser and the receiving position of the detection point are changed to excite the ultrasonic wave again; when the surface wave reflection signal is received, it is indicated that a surface crack exists near the probe point, the time T1 taken by the probe point to receive the surface wave for the first time is recorded with the time zero point at which the laser starts to enter, and the time T2 at which the surface wave is received, and the distance x between the crack and the laser incident point can be obtained from the equations (1) and (2).

When a crack exists, the laser-excited surface wave reaches the bottom of the crack and is converted into a transverse wave to propagate in the material, as shown in fig. 5. If the laser incidence point and the detection point are close to the crack, the surface wave reflection echo Rr and the surface wave R are subjected to aliasing, and the acoustic time measurement error is large; if the laser incidence point and the detection point are far away from the crack, the obvious echo waveform is not easy to see at the detection point due to the attenuation of the acoustic wave. Therefore, when the reflected surface wave is detected, the laser incidence point and the detection point need to be adjusted continuously, and a proper laser incidence point and the detection point are selected for crack detection.

And (3) recording the distance m between the probe point and the incident point of the laser, recording the time T1 for receiving the surface wave for the first time, recording the time T2 for receiving the reflected surface wave by the probe point, wherein the time for receiving the bottom surface reflected transverse wave by the probe point is T3, and obtaining the size h of the crack according to the formula (6).

In summary, the method for identifying the position and size of the crack on the metal surface based on the thermo-elastic effect provided by the embodiment of the invention has the following advantages:

(1) for materials with unknown solid mechanical parameters, various ultrasonic sound velocities can be measured, and then crack defects can be detected and positioned, so that the application range is wider;

(2) various ultrasonic waves excited by laser are fully utilized for crack defect analysis, so that the position and the size of a crack can be determined, and further the qualification of a manufactured part is evaluated or whether in-service equipment needs to be replaced and maintained is determined;

(3) the method mainly utilizes the surface wave generated by the thermo-elastic effect to detect the crack, and combines the graph 3 and the graph 4 to obviously see that the change of the received signal of the detection point can be observed more intuitively and sharply by utilizing the surface wave analysis, so that the crack detection sensitivity is higher.

Furthermore, the terms "first", "second" and "first" are used for descriptive purposes only and are not to be construed as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one such feature. In the description of the present invention, "a plurality" means at least two, e.g., two, three, etc., unless specifically limited otherwise.

In the description herein, references to the description of the term "one embodiment," "some embodiments," "an example," "a specific example," or "some examples," etc., mean that a particular feature, structure, material, or characteristic described in connection with the embodiment or example is included in at least one embodiment or example of the invention. In this specification, the schematic representations of the terms used above are not necessarily intended to refer to the same embodiment or example. Furthermore, the particular features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples. Furthermore, various embodiments or examples and features of different embodiments or examples described in this specification can be combined and combined by one skilled in the art without contradiction.

Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention, and that variations, modifications, substitutions and alterations can be made to the above embodiments by those of ordinary skill in the art within the scope of the present invention.